The most common method and apparatus for reducing the temperature of living spaces and the like during the warmer months, commonly called air-conditioning methods and apparatus, involve the use of a refrigerant, means for compressing the refrigerant, means for removing heat from the compressed refrigerant, and a cooling coil into which the compressed refrigerant is expanded and vaporized. This coil is commonly called an expansion coil or refrigerating coil and the room space is cooled by blowing air across such coil and discharging the air through a duct system involving various outlets in various locations in the living space. Because of the cost of operating this type of refrigerating system, it is the common practice to re-circulate most if not all of the room air, so that precautions must be taken to avoid building up to excessive moisture in the air system. Moisture is normally removed by cooling the air at the refrigerating coil to the dew point or below and removing the resulting condensate.
In regions of low relative humidity the low wet bulb temperature such as the southwestern part of the United States, so-called evaporative coolers have gone into rather extensive use. For the most part evaporative coolers provide for no re-circulation of air whatsoever, the outside relatively dry air being brought in at a relatively high rate of speed and passed through moist pads to thereby cool the air adiabatically; that is to say, to reduce the sensible heat as shown by the dry bulb thermometer and increase the latent heat as shown by the wet bulb thermometer. The sensibly cooler air that has entered the living area replaces the room air which is vented through slightly open windows or doors in various parts of the house to provide uniform distribution of replacement air. There are many advantages in the use of evaporative cooling, particularly in intial cost, since the system is simple and requires no appreciable duct work and no returns. The actual operating costs are low because the water and power required to operate an evaporative cooler together cost much less than the power required to operate a refrigeration system.
Evaporative coolers are known to have certain disadvantages and limitations. For one thing, there is no reduction of total heat and there are circumstances under which this fact becomes discernible. The evaporative cooler also introduces amounts of additional moisture into the air but no build-up of moisture such as caused by re-circulation. There are times when the actual moisture in the system introduced by evaporative cooling may be too great for comfort, particularly during periods of relatively high humidity such as is encountered at certain times even in the most arid areas. There may be only a very few days in arid areas where the moisture of the air will be high enough to bring discomfort, but in borderline areas the total percentage of time during which unduly high humidities will be encountered may be great enough to make the use of straight evaporative systems undesirable or impractical.
In addition, persons suffering from allergies to pollens and molds are adversely affected by the constant introduction of outside air. Very often the development of molds in the evaporative cooler itself further aggravates the problem.
Nevertheless, in the current period of rising energy costs and fuel shortages it is highly desirable that every advantage possible should be realized from the inherent efficiency of the evaporative cooling approach.
What is needed, therefore, is a simple, effective, efficient and inexpensive cooling or air-conditioning system based on the principles of the evaporative cooler but avoiding the stated disadvantages thereof.